The present invention relates generally to medical catheters. More specifically, the present invention relates to catheters which can be used to deliver a stent to a deployment site in the cardiovascular system of a patient.
Stents are devices deployed in the cardiovascular system of a patient to maintain the patency of a vessel at the site of a lesion. Typically, this requires advancement of the stent through the cardiovascular system and then deployment of the stent at a stenosis site in the vessel where the lesion has developed. A balloon-expandable stent is delivered by securing it onto a balloon of a delivery catheter which then may be advanced through the vascular system to the stenosis site. Once at the stenosis site, the balloon is inflated to deploy the stent.
Significantly, the delivery catheter must bend in different directions as it follows one of the tortuous routes through the vascular system to the stenosis site. As the catheter bends, the attached stent will also bend, and the ends of the stent may deform and flare outwardly from the balloon, thereby increasing the profile of the stent. With such an increased profile the stent may not advance further through the cardiovascular system to cross the lesion site, or the stent may not be easily withdrawn from the body, if that is desired. It is preferred that the stent be retained snugly against the balloon until the stenosis site is reached. Once the stent is placed across the stenosis, the stent should quickly and easily separate from the catheter after the balloon inflates during the deployment of the stent.
Various devices have been proposed to retain the stent against the balloon in a delivery catheter. In several prior art devices, pairs of separate sleeves, caps or cuffs are mounted over the stent proximal and distal ends to prevent their premature expansion. In one of such devices, the cuffs are mounted on a stent-carrying, tubular cartridge which may be slid over the balloon of any suitable stent delivery catheter. In another prior art example, the ends of a balloon-mounted stent are overlaid by cuffs formed from excess material of the balloon.
In yet another prior art device, retention sleeves self-retract from their positions overlying the ends of the stent during inflation of a balloon. In this case, the sleeves are anchored to a catheter shaft, and they need to fold or accordion to reduce their overall length while sliding down the cones of the expanding balloon. For the devices mentioned above, the ends of the stent must slide out from under the end caps as the balloon expands the diameter of the stent.
In yet another device, a stent is mounted on a delivery balloon that has been wrapped with elastic material, and slidable caps cover the ends of the stent until the balloon is inflated. However, in all devices that utilize stent end caps, the stent may fail to completely exit from within a cap during deployment, possibly leaving the cap caught between the stent and the vessel wall after the balloon has been deflated. To avoid this problem, the end caps may be mounted with only a short overlap of the stent ends, which can lead to premature uncovering of the stent ends and concomitant loss of retention.
With the above in mind, it is an object of the present invention to provide a catheter for delivering a stent which retains the stent snugly against the catheter balloon during advancement into the vascular system.
In accordance with the present invention, a device for retaining a stent on the balloon of a delivery catheter includes a flexible, elastic sheath, or sleeve, that is positioned over the balloon on the delivery catheter. After the stent is crimped into place over the sleeve, circumferential folds of sleeve material are formed to lie over the ends of the stent and thereby hold the stent on the balloon until it is deployed. During deployment of the stent, the inflation of the balloon stretches the sleeve, essentially eliminating the folds and thus ensuring release of the stent from the catheter. The invention features a reliable mechanism to withdraw the retention folds from the ends of the stent during deployment, such that the folds of the present invention can cover wider margins at the ends of the stent than were previously advisable, thus providing more dependable retention of the stent on the catheter.
In a preferred method of making the present invention, a balloon delivery catheter is provided with its balloon uninflated and wrapped, or furled. While the balloon remains wrapped, the sleeve is positioned over the balloon, and the stent is crimped onto the balloon-sleeve combination. The ends of the sleeve are then bonded to the catheter adjacent the ends of the balloon. The sleeve material is gathered and formed into folds adjacent the ends of the stent.
Next, the proximal fold is pulled in the distal direction and folded over the proximal end of the stent, and the distal fold is pulled in a proximal direction and folded over the distal end of the stent. The folds are then heat set to hold their shape. Thus, the sleeve is formed with a distal fold and a proximal fold, both of which are used to help retain the stent in place around the balloon. The sleeve is preferably made of an elastomeric material such as a low durometer synthetic rubber.
The heat setting process is preferably provided using heat-shrink tubing to provide compression force during heating. In addition to setting the folds over the ends of the stent, the heat and compression can also be used to embed the folds into the stent to establish a firm grip on the stent. The heat setting process also reduces the profile of the catheter to facilitate insertion of the delivery catheter into the cardiovascular system of a patient.
In operation of the present invention, a delivery catheter with sleeve and stent are advanced into the cardiovascular system of a patient until the stent has been properly positioned within the stenosis for deployment. During this advancement, the ends of the stent are held in a restrained position against the deflated balloon by the proximal and distal folds in the sleeve. After the stent is properly positioned, the balloon is inflated to expand the sleeve and the stent. The expansion of the balloon causes the proximal and distal sleeve folds to unfold and smooth out, withdrawing the folds from over the ends of the stent. Subsequently, as the balloon is deflated for removal of the delivery catheter from the patient""s cardiovascular system, the elastic sleeve contracts along with the balloon, thus assisting in the re-wrapping of the collapsing balloon. The result is an overall reduction in the profile of the sleeve and the deflated balloon. The delivery catheter, with its reduced deflated balloon profile, is withdrawn from the patient while the stent remains deployed in the patient""s vessel